U Frame coax OB with side mounted bass drivers (Blade).

[sfdoddsy]

For WAF reasons, I'm looking at creating the most compact open baffle possible using my existing SEAS C18s and Dayton RS225s.

One shape that I'm considering is a bookshelf U frame with side mounted bass drivers.

Something like this:



I need it to get to below 80Hz before going to a sub.

From what I've been told, this bass payout may help with rear cancellation (quasi-cardiod) which would help with wall positioning.

But would there be any real benefit or would I be better off just sticking a bass driver on the front below the coax?

All thoughts appreciated.

[Juhazi]

Hi,
small speaker as dipole is practically impossible to do. Midrange should have minimal baffle, so sideplates shoud have vents. Bass is something that I cant get hold on, dispersion is very difficult to estimate but I'd guess that it is basically a sideways dipole with minimal baffle - worst scenario...

You call this bookshelf speaker. Do you mean its size or will you put it on the shelf? Dipole needs at least 80cm to walls to work as intended and to make reflections in the right way.

If you want to have something dipolish, let the midrange be open and make a closed box for woofers. 2x Dayton RS225 will play loud and low with eq. That way you will get cardiod sum with cancellation on the backside, around crossover frequency of woofer and mid. Dsp-xo is only reasonable choice, because xo is impossible to make by simulations.

[Jonasz]

I would make a "small" floorstander if I were you. Similar to SBAcoustics dipole design from the Munich show. Two 15" ripole on top of each other and on top of that a minimal baffle for the C18. If you squeeze a bit you should be able to get away with a 100×20×40cm design wich is easy to disguise as a box speaker.

[sfdoddsy]

It's going to be a stand mounter.

The way I figure it my old Orions with s single 8 inch driver on flat baffle got me down to 90Hz or so, so with a folded baffle I should be able eke out a few more Hz.

[Juhazi]

The U-frame dipole should have the driver at the bottom of U. In your sketch acoustic pathlength to where front-and backwave meet is almost like with no baffle on the backside. Asymmetric setting of a dipole driver can be simulated with The Edge easily, but U-frame cannot. Alas the null bets angled towards the listener or front-wall in your sketch, like in Gradient Helsinki 1.5

Place bass drirvers on top of each other or make a M-shape sub-frame like LX521 has. Here is my quick and dirty simulation of it's response



Dipole origami https://www.hifizine.com/2012/12/subwoofer-origami/

[sfdoddsy]

Thanks, this is what I'm trying to work out.

The layout I posted was suggested by a chap with his own corporate circle at Audiocircle and since I've had disagreements with him in the past I couldn't ask about it there.



Since I've never seen the layout before it seemed to good to be true and from your simulation is.

I could EQ everything flat, but if there is no advantage over one driver on the front what is the point?

[Juhazi]

Hm, my proposal is U-frame with drivers on the bottom of U. In edge simulation sidewings are spread out. Still, this is not very reliable, because in U-frame backside radiation gets some boost from the cavity and it will have some resonances. Only a deep U-frame (like a tube) with stuffing will work as cardioid, but not this kind of shallow U.

U-frame with drivers near edges is questionable, because I am afraid that the real radiation pattern with U-frame will not be dipole, because there is no direct radiation towards he listener at all.

These ad hoc special dipoles are interesting anyway. Prototypes should be measured first, You can use thin plywood or particle board sheets, just fix them sufficiently to avoid resonances.

[sfdoddsy]

After further investigation, I've discovered that the chap who made the suggestion subsequently discovered that the layout didn't act like an open baffle, but as a large slotted port with more output to the rear.

So not much point to it.